Pls, How do I block a particular site in Mikrotik router(ROS) configuration. I mean through winbox

How can I block every site, then make exceptions to the few sites that I want to allow access to?
thanks

Follow the guide in that link. But instead of a blacklist (specific deny on certain sites) configure a whitelist consisting of accept statements for the sites you want to allow followed by a blanket deny for a wildcard ("*").